This invention relates to irrigation systems, and more particularly, to systems for controlling operation of irrigation systems.
In a system of the type disclosed in U.S. application Ser. No. 746,456, now U.S. Pat. No. 4,108,200, entitled "BRAKE APPARATUS FOR IRRIGATION LINE" (assigned to the Assignee of this invention), apparatus for maintaining the alignment of an irrigation line is provided. As disclosed therein, a link is operatively associated with a relatively openable and closable valve, the link reading the degree of misalignment of portions of the irrigation line to in turn open and close the valve to supply increased and decreased water pressure to the rotary water motor as needed. While such a system has been found highly effective in maintaining proper alignment of an irrigation line, it has been found that under certain situations, in particular, at lower drive speeds of the irrigation line, one or more rotary water motors will stop rotating for a short period of time, meanwhile with water still exiting therefrom onto the field. It will be understood that even distribution of the water from the irrigation line is highly desired, and the state just mentioned, wherein water exiting from the water motor falls on one small area for any length of time, is to be avoided.
Additionally, reference is made to the U.S. Pat. No. 3,750,696 entitled "MAYDAY SAFETY SHUTOFF SYSTEM RESPONSIVE TO ERRANT TOWERS OF AN AUTOMATIC IRRIGATION SYSTEM" (assigned to the Assignee of this invention), disclosing as one embodiment thereof a safety shut-down system wherein a main valve is shut upon loss of pressure in a safety line. Such loss of pressure in the safety line occurs upon excessive misalignment of portions of the irrigation line. In the application of such a safety system to a center-pivot irrigation system, if for some reason the main valve does not close off upon a relatively high degree of misalignment being reached, the outer end water motor of the system continues to drive the end tower thereof, increasing the misalignment so that damage to the system occurs. United States application Ser. No. 700,226, now U.S. Pat. No. 4,067,497 entitled "SPEED GOVERNOR FOR IRRIGATION SYSTEM" (assigned to the Assignee of this invention) discloses in general a center-pivot irrigation system including a governor operatively associated with the outer tower and rotary water motor thereof.